Cathode ray tube titration apparatus



MCB 5, 1940 G. F. SMITH CATHODE RAY TUBE TITRATION APPARATUS Filed Nov. 27, 1936 5 Sheets-Sheet l Man-mh 5 w40. G. F. sMrrH 2,192,777

GATHODE RAY TUBE TITRATION APPARATUS Filed Nov. 2?, 1936 3 sheets-sheet 2 GA'IHODE RAY TUBE TITRATION APPARATUS Filed Nov. 27, 193e?- l s sheetsfsheet'a 25a I I I 0a 7` e 655 15j/23170325 Pke SuppJy-Z 755.5 200- efSPZQ/Pfszsr-z@ f 0 0 es D 1% 15@ 60?; 5

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gmc/wiwi Georyeederz'o' 5512 ik @www 50 ammeter of a continuous Patented Mar. 5, 1940 YUNITED t STATES PATENT OFFICE CATHODE RAY TUBE TITRATION APPARATUS Application November 27, 1936, Serial No. 113,048

2 Claims.

This invention relates to potentiometric titration apparatus of the type utilizing electronics in the actuation thereof. Application of the vacuum tube or triode to the eld of electrometric titra- 5 tions has resulted in the simplification of such apparatus in that the progress of the titration can be followed continuously and automatically and without the employment of a potentiometer used in earlier electro-titrationapparatus. Such lo electronic titrimeters may be used advantageously in the broad field of controlling and noting various chemical reactions as precipitation, neutralization and oxidation-reduction.

Electronic tubes have been used in`such apparatus for some time and have now reached a point of development where the same may be connected with and operated by standard commercial electrical circuits, dispensing with the use of batteries or current developing cells. However, the most advanced electro-titrimeters employ in conjunction with the electronic 4tube amplication sensitive and relatively expensive micro-ammeters, and it is the object of the present 'invention to further improve such electro-titrimeters by the elimination of the micro-ammeter, utilizing in lieu thereof a cathode ray tube as the indicator.

Among other objects'of the invention are: the

. Yprovision of an electronic-titrimeter of the direct reading line-operated type in which an expensive and easily injured micro-ammeter is not required; the provision of a titrimeter wherein the com'- plete apparatus assembly is self contained, sturdy and readily portable, having a total cost which slightly exceeds that `cnf the micro-ammeter hitherto employed in all line-operated thermionic titrimeters; the provision of titrimeter apparatus so constructed as to possess a high degreerof resistance against injury due to accidental or faulty o manipulation; the provision of a titrimeter which can be used in connection with either (a) the mono-metallic, externally polarized electrode system or (b) the bi-metallic self-polarizing system,

or (c) the usual half cell and reference electrode system; the provision of a titrimeter of the character desired wherein the sensitivity of the potential change indicating mechanism is far greater than the usual electron tube amplication ar` rangement as applied to the conventional microindicator system, whereby through .said increased sensitivity not only is one able to determine continuously the progress of the reaction under determination but also to gain a denite indication of the reaction velocity;'a titrimeter wherein analytical reactions 'of'an improved indicator for titrimet'ers wherein no moving parts are involved and wherein instantaneous response of the indicator to applied impulses is obtained and immediately readily discernible, and other features v of operation, con- 15 struction and arrangement which will be in part obvious or pointed out hereinafter. A

For 'a further understanding of the invention, reference is to be had to the following description and the accompanying drawings, wherein: 20

Fig. 1 is a perspective view of the cabinet in which the apparatus comprising the present in-k vention is contained; I

Fig. 2 is a vertical sectional view taken through the cabinet and disclosing the interior appara-4 25 tus; w J Fig. 3 is a horizontal sectional Vview of the cabinet, with the apparatus therein disclosed in. P19111;

Fig. 4 is a diagrammatic'view of the several cir- 30 cuits utilized by the present invention;

Fig. 5 is a similar viewof the cathode tube.

Fig. 6 is a diagrammatic view disclosing a graph illustrating variation in shadow angles and plate current at diilerent bias voltages of va cathode ray tube. y

Among -the recent developments in electronic tube manufacture is the so-called cathode ray tube, which has been quite widely used as the visual timing indicator in modern radio receiving sets. commercially the tube is known as the 6E5 or the magic eye tube. 'I'his unique tube, actually two tubes lin one, consists of a triodev section or amplier, in the top of which is mounted a miniature cathode ray tube. A concave disk electrode near the top of the tube, designated the fluorescent screen or target, glowsas a greenv fluorescent circular area when the tube is in operation. 'I'he cathode,v common to both tube sections, extends into and above the target and terminates in a black button-like shield in the top of the tube. In such a tube, the electron beam is produced and controlled as follows: With the cathode heated, and 200 to 300 voltsapplied'to the concave disk electrode or M target, a screen of electrons from the cathode bombards the target electrode causing the fluorescent screen to glow with a greenish coloration. A ray controlling electrode or deflecting plate is connected to the plate of the triode section of the tube and extends through and into the confines of the target electrode. The ray con-1 trolling electrode or deecting plate is mounted very\ close to the cathode and is thus interposed in the beam of electrons streaming to the target. Depending upon its potential, the ray controlled electrode or deflecting plate serves to deflect the electron streams from their original paths. This deflection is -made evident by the appearance of a sector of shadow on the fluorescent target, there being no electrons in the restricted beam or beams to cause iluorescence.

Since the ray controlling electrode or deflecting plate is connected directly to the triode plate, its potential varies directly with it. \With decrease in negative grid bias, the triode plate current in'- creases, increasing the voltage drop in the resistance R12' (see Fig. 4) thus lowering the potential of the ray controlling electrode. With this condition, there is a maximum deflection'of the electrons appearing on the target as a maximum shadow. The angle of the shadow varies from 90 to 100 at zero bias, to 0 at negative 8.5 volts bias applied to a triode grid of the cathode ray tube.

This combination of the triode and cathode ray t'ube becomes essentially a self-contained vacuum tube voltmeter in which the cathode ray tube replaces the expensive micro-ammeter ordinarily used in apparatus of this character. The versatility and adaptation of such a combination are Y at once apparent, particularly in view of .the rapid response to applied E. M. F., because there are no mechanically moving parts as in prior *of a cabinet 2 with the other end of the glass shell 3 of the tube projecting through an opening in the removable front panel 4 of the cabinet so that the uorescent target 5 of the cathode 2 may be viewed from the front ofthe cabinet.

YThe contact prongs 6, which project from the base 1 of the tube, are received within a socket member 8 carried by a stationary bracket 9 projecting upwardly and vertically from a horizontally disposed supporting shelf- I0 which is sta- ',tionarily connected with the front panel 4 of the cabinet and is adapted to support the apparatus contained within said casing, so that upon lremoval of the front panel from the casing, all

interior apparatus will be readily accessible.

A cathode ray tube-such as indicated at I, is a standard commercial product `and therefore an extended and detailed description of its construction and operation need n ot be given herein.

However, to facilitate a clear understanding of the present invention,A the following brief description regarding the construction and operaplate or ray control electrode II is connectedto the triode plate I2 as indicated in the diagram. These two elements are connected to the target electrode 5 through a 1 megohm resistor indicated at I3. If `zero bias be now applied to the triode section of the tube, the maximum plate current will flow to the triode plate. This current ows through the resistor I3 and thereby produces a voltage drop between the target 5 and the deilecting plate II.

Since the plate is negative with respect to the target, it will reduce the number of electrons reaching the target. Because of the shape and location of the deflecting plate, a shadow will be cast around the target. The shadow angle will be about 100.

current'will decrease somewhat, decreasing the voltage diierence between the target and the deecting plate, resulting in the shadow angle closing in since not as many electrons are repelled as before. After two volts bias is applied, the shadow angle change per volt bias applied to the grid increases somewhat and remains constant until about'six volts bias is applied. From six to eight volts, the rate of change slows up somewhat but at eight volts, the shadow has usually entirely disappeared.

In Fig. 6, there has been shown a graph which illustrates how theshadow angles and the plate current of the triode vary if different bias voltages are applied to the triode section.

A schematic diagram of the circuit employed by the present invention in which the cathode ray tube indicator is utilized, is shown in Fig. 4. The design of the circuit and the arrangement thereof represent a compromise between sensitivity, stability and linearity of response, together with the use kof A. C. line power. The present circuit has been laid out with particular reference to. oxidation-reduction titrations using the bimetallic system, with potential breaks of 100 to 200 millivolts. Since a change of about 8.5 volts is required to completely operate the shutter or indicator, as above pointed out, a voltage amplication of 100 is necessary. This has been realized by the' use of a voltage amplifying vacuum tube I4, with the output of this tube operatingthe cathode ray tube I. The tube I4 is known commercially aa a '77 high mu pentode tube.- A variable sensitivity controlled rheostat R10 is employedto control the output of the tube I4 in order that the break in applied E. M. F. suffices to operate the shadow. The rheostat or resistor Rw serves to positively bias the triode grid-I5 of the tube I and, therefore, it is necessary to balance out this potential by an opposite potential developed across the resistance or rheostat R5. In order to realize maximum simplicity in adjustment, the resistances R5 and Rm have been grouped and are controlled from a single operating shaft, indicated at I6. There are iive tapped positions providing five adjustments in sensitivity and allowing a full 90 movement oi the shadow for applied E. M. F. breaks varying between 100 and 300 millivolts. Under these conditions, the cathode ray tube is maintained in an essentially sensitive condition irrespective yof the sensitivity'setting.

An additional manually operated indicator conf trol R2 is used to balance out the initial potential If the bias is increased slightly to approximately two volts, the plate developed by-the titrating cell and bring the` indicator shadow to an initial setting at the start of ja titration. The operating knob of the 2,192,777 .resistor R2 is indicated at I'I in Fig. 1 of the drawings, while the corresponding knob for the resistances R5 and R10 is indicated at I8. These two manual controls take care of all necessary adjustments of the shadow and breaks in applied E'. M. F. Under these conditions, the position of the shadow yof the tube I is at all times controlled by the net bias of the amplifier tube I4 which is maintained at the same value at the center of all titrations regardless of the potential developed across the titrating cell. An essentially constant sensitivity is thus realized over any reasonablerange of initial potentials.

Provisions are also made for use of the apparatus with an externally polarized mono-metallic .(Pt.-Pt.) electrode system. A polarizing current of approximately 1.5 105 amperes is bled from the resistances R1 and Rz by shunting the latter directly across the titrating cell I8 through a 300,000 ohm resistor R1. This method of obtaining the polarizing current is entirely practical as the internal resistance of the titrating cell is negligible incomparison with theresistor R1, so that the operating bias on the amplifier tube I4 is only slightly affected. A manual controlling switch for this circuit is indicated at I9, this switch being of any conventional on and off type.

The 500 volts of direct current supply is obtained from the vacuum tube indicated atA 20. This tube commercially is known as the type and is connected as a half wave rectifier with which adequate lter and bleeder resistors furnish all grid, screen and plate voltages. It should be noted that the cathode of the cathode ray tube I operates preferably at 200 Ato 300 volts to ground and that a separate heater winding must be used.

In actual use, the above circuit is suiiiciently stable for all potentiometric titrations. For that reason, increased stability obtained by application of a bridge or mu-balanced principle has not been deemed necessary, especially as equilibrium voltages are not required. Line uctuations of vevolts introduce enough variation to operate the shadow of the cathode tube. Such an extreme variation during a titration may for all practical purposes be considered remote. A` gradual drift of the shadow, especially during the. warming up interval following the initial heating of the tubes may be noted; random uctuations, however, are scarcely discernible. The sensitivity is such that most practical titrations using the bi-metallic system will cause a significant movement of the shadow generally a full In other words, for maximum sensitivity, a, change in applied E. M. F. of millivolts will cause a full 90 change. Angular displacements of 10 to 20 can be noted readily, so that end-point changes considerably tube. `A circular metal frame 2I rotatably adjustable about the longitudinal axis of the exposed end of the tube I can be provided with a scale of 90 range with 5 intervals to correspond t'o the various degrees of opening of the wedge-shaped non-fluorescent area of the cathode ray tube.

Its calibrations should be made after the ray tube is mounted and affords a convenient means for noting the variations in the sector shadow. The control knobs and their associated dials for the citing potential changes.

resistances R5, R10 and R2 are mounted at either Vside of the middle portion of the panel below the exposed end of the cathode ray tube and spaced substantially equi-distantly from the latter.

The left hand dial or knob, when viewed as in Fig. 1, controls the sensitivity of the cathode ray Atube to applied E. MTF. At setting 1 of this dial. the non-fluorescent screen sector can be increased from 0 to 90 with an applied E. M. F. of 100 millivolts. Since unmistakable equivalence point sector displacements of 45 are entirely satisfactory, end point breaks of 50 millivolts are ample in At a setting of 5 for sensitivity control, the same sector displacements of the cathode ray tube require 300 millivolts; Since this is approximately the maximum equivalence point"break for titrations of reductants of low oxidation potential by oxidants of high oxidation potential, the range covered is ample and could be further increased if desired. values were substantiated using a standardized potentiometer circuit and the relationships were shown to be sensibly linear over the entire working range of the sensitivity control.

The right hand dial control, when the apparatus is viewed as in Fig. 1, employed for governing the resistance R2, operates the setting of the initial reading of the non-uorescent wedge sector at the beginning of a titrational operation. In case a particular titration proceeds to the equivalence point with an appreciable change in potential, this dial setting may be changed during the progress of the titration. This scale setting is of value in checking the duplicationvof starting and final potentials.

The centerlswitch I9 in the lower central part of the panel 4 is the off and on switch of the polarizing circuit. The electrode connections for the titrating cell I8 are shown in the lower left side of the panel, when viewed as in Fig. 1 and extension cords 22 unite the same with the titration cell. The operation of the variable tube secy p the.loWer right h-and corner of the panel as when viewed in Fig. 1, the fuse being replaceable from the front. A A. C. power line connecting plug 24 is connected with the apparatus and the switch of this power circuit is made a part of the sector setting dial control. .The uorescence of the cathode ray tube gives excellent contrast with the non-fluorescence sector space in articial light and in direct daylightof ordinary intensity. Lecture demonstration using the cathode ray tube may be facilitated by employing a flexible cable to connect and separate cathode ray tube to the apparatus assembly, so that the cathode ray tube may be disposed remotely with respect to the cabinet apparatus.

From the foregoing, the practical advantages to be derived from; the use of the present invention will be apparent, itis believed, to those skilled in the use of apparatus of this type. The practical results from the elimination of vthe milla-ammeter used in the previously described electronically operated potentiometric equipmentare at once apparent. With one( unit of equipment, the present invention makes available a titrimeter which applies the cathode ray tube to substitute for the use of the milla-ammeter of other continuous recording titrimeters which can be powered by a single 110 volt A. C. line source. The

apparatus comprising the present invention can be used with any previouslyemployed electrode system. The calomel or silver chloride electrode and platinum electrode may be used. The monometallic (Pt-Pt.) electrode system using the polarizing current control aiorded by the present invention is operative with equal facility. The much to be preferred Pt.-W self-polarizing electrode system is ideal.

The advantage in the use of the presentV invention is most apparent, due to the instantaneous response of the cathode ray tube sector shadow to changes in potential in the titration cell. rIfhis has the double advantage that the warning of the approach to the equivalence point during titration is greater than would be possible through using a continuous reading milla-ammeter with its moving parts and which are inherently sluggish in responding to applied impulses. In the same manner, the velocity reaction in titrating cell is at once apparent. A 'reaction which is too slow, due to incorrect acidity, temperature, etc.4 is readily noted and proper adjustment can be made. For the'same reasons, a color indicator end point determination is not as satisfactory. 'I'he warning of the approach to the end point is not nearly as good and almost no indication of the rapidity of the reaction is afforded with a color type of indicator. Again, all oxidation-reduction indicators are not reversible which is not true of the end point' determination afforded by the present invention.

If it is desired to read 'the actual potential of the titrating cell throughout the progress of the titration, such a working potential at any time may be conveniently determined by'the *usel oi a simple potentiometer with direct reading scale, supplied as an accessory. The use of an extension cable and auxiliary cathode ray tube enables one, by placing it alongside of the titration beaker, to observe the effects of the dropwise circuit of reactants without glancing from the titration beaker to the cabinet assembly. The effect is the same as that obtained when using a conventional color indicator. The present invention may be used advantageously as a part of the equipment of research and routine analytical laboratories as well as in instructional or educational institutions interested in the teaching of instrumental methods of analysis.

What is claimed is: f

l. In electronic titration apparatus, means for measuring the voltage of a titrating cell circuit 4having a pair of electrodes, an amplifying circuit for connection with said- .cell circuit com- "prising a pentode electronic tube amplifier having an input circuit andfan output circuit, variable resistance means connected inthe input circuit of said amplifying circuit for series connection with'said.A electrodes, variable resistance means in the output circuit of said pentode tube amplier, a cathode ray electronic tube coupled with said amplifying circuit comprising an electron emitting cathode, a plate, a control grid, and a uorescent target, said resistance means in the output circuit of the amplifying tube variably biasing the grid of said cathode ray tube, and additional variable resistance means between said pentode amplifying tube and cathode ray tube adapted to be adjusted conjointly with the variable resistance in the output circuit of the pentode ampliiler foradjusting the sensitivity of the cathode ray tube for different conditions in said input circuit to give a substantially constant range of indication on said fluorescent target.y

2. In electronic titration apparatus, means for measuring the voltage of a titrating cell circuit, an amplifying circuit for connection with said cell circuit comprising a thermionic amplifier having an input circuit and an output circuit, variable resistance means connected in the input circuit of said amplifying circuit, variable resistance means in the output circuit of said titrating amplier, a cathode' ray electronic tube coupled with said amplifying circuit comprising a control grid and a iluorescent target, said resistance means in the output circuit tube of the thermionic ampliiier variably biasing the grid of said cathode ray tube in accordance with varying conditions in said titrating cell circuit, and additional variable resistance means between said thermionic V l tion on said fluorescent target, said first-mentioned variable resistance means in the input circuit of said thermionic amplier serving to balance out the initial potential developed by the titrating cell and to bring the indicator shadow on the iluorescent target to an initial setting at the start of titration.

GEORGE FREDERICK SMITH. 

